13 Common Causes Of Sudden, Unexplained Weight Gain

But before you go looking for answers, see if you can find an explanation for your unexplained weight gain.

Before visiting the doc, keep a log of everything you eat as well as your exercise habits (including activity outside of your workouts) for at least a few days if not a week or two, says Melina Jampolis, M.D., an internist and physician nutrition specialist based in Los Angeles.

Maybe youre eating more calories now, or youve spent weeks sitting down more than usual thanks to a heavier workload. If you still cant seem to figure it out, your doc can help you get to the bottom of whether any lingering health issues might be messing with your waistline.

There are tons of reasons for unexplained weight gain besides eating more and moving less. Heres a list of conditions that could be causing your sudden weight gain, and how to tell if its time to see a doctor.

Hypothyroidism

When a young woman walks into a docs office with unexplained weight gain, the thyroid is the first place most physicians will investigate, says Jampolis. And for good reason: a whopping one in eight women will develop a thyroid disorder in her life, according to the American Thyroid Association .

That butterfly-shaped gland in the neck is responsible for secreting a hormone that regulates the metabolism, and if youve got an under-active thyroid (called hypothyroidism) the metabolism may slow down, triggering weight gain.

Women with hypothyroidism may also suffer from low energy levels or fatigue, dry skin, hair loss, hoarseness, or constipation, says Jampolis. Notice any of them and you should book a chat with your doc who can check on your thyroid with a simple blood test if necessary.

Polycystic Ovary Syndrome.

Research shows that as many as one in five women have polycystic ovary syndrome (PCOS)an endocrine disorder that throws off the balance of reproductive hormones estrogen and testosterone, and can trigger a number of unpleasant symptoms like wacky periods, facial hair growth, and migraines.

PCOS can also muck up the way your body uses insulin (the hormone that helps turn sugars and starches into energy), which means (womp, womp) unexplained weight gain around the mid-section is common, says Jampolis.

If your menstrual cycles are off, a gyno will likely take a peek at your hormones to diagnose this one.

Depression or Anxiety.

When you're chronically stressed , you're thrown into fight-or-flight mode and get a surge of adrenaline, along with a heavy dose of the hormone cortisol, which is supposed to help you restore energy reserves and store fat. Because, hello, you just sprinted three miles from a tigeryou're starving.

The problem? Lots of us get stressed sitting at our desk, says Jampolis.

If youve persistently felt down in the dumps or anxious, have trouble sleeping, feel fatigued, or youve lost interest in the stuff that used to make you tick, talk with an M.D. or mental-health pro who can make suggestions for getting back on track, which (bonus) should help you drop those extra pounds.

Insomnia.

Theres nothing like a busted night of sleep to make a girl crave sugar and fat (anything to survive at work the next day, right?). That's because missed shuteye does a number on your hunger hormones and metabolism: Sleeping too little raises ghrelin, the hormone that signals its time to eat, while lowering your levels of leptin, the hormone that conveys the Im full feeling, says Jampolis. The result: a totally unsatisfying chow-fest the next day.

Putting off sleep to watch just one more episode? That hour could be contributing to sudden weight gain. A 2018 study in the journal Sleep found that people who slept just one hour more per week lost more fat than those who slept an hour less. The people who slept less lost lesseven though everyone in the study ate the same number of calories, proportionate to their weight at the start of the study.

Small Intestinal Bacterial Overgrowth

The gut relies on good bacteria to function well ( probiotics , anyone?), but theres also bad bacteria chilling in your digestive tract. When that balance of good to bad gets thrown off, small intestinal bacterial overgrowth (SIBO, for short) can take place, triggering extra gas in your GI tract along with bloating , abdominal pain, diarrhea, andyou guessed itsudden weight gain.

Docs arent entirely sure how SIBO may trigger those extra pounds, says Jampolis, but treatment for SIBO typically includes antibiotics to treat the bacterial overgrowth, according to the U.S. National Library of Medicine .

Perimenopause.

The transition period to menopause (a.k.a., perimenopause, which can start in women as early as their mid-thirties, but usually starts in your forties) triggers hormones like estrogen to rise and fall unevenly, which can cue weight gain in some women, says Jampolis. (Other signs of perimenopause include irregular periods, hot flashes, mood swings, and a change in your libidosymptoms your doc can usually suss out with her eyes closed.)

Compound perimenopause with the other inevitable body changes that happen with age (like a loss of muscle mass and increase in body fat), and it may feel like the scales tipping fast. Talk to your doctor to manage "the change" in stride.

Medication

There's a laundry list of both prescription and over-the-counter meds that can trigger sudden weight gain or water retention that shows up on the scale as extra poundage. Antidepressants most commonly the selective-serotonin reuptake inhibitors (SSRIs) such as Paxil, Lexapro and Prozacmay affect the appetite center in the brain, says Roco Salas-Whalen, M.D., an endocrinologist at the Medical Offices of Manhattan .

Meanwhile, beta-blockers (meds that reduce blood pressure) can slow your metabolism, and certain steroids (like prednisonean anti-inflammatory that causes water retention and an increase appetite) can add on pounds. Even OTC antihistamines like Benadryl, which can disrupt an enzyme in the brain that helps regulate food consumption, can trigger noticeable weight gain, says Salas-Whalen.

A word to the wise: Dont stop taking any pills cold-turkeychat with your doctor, who may be able to find a more waist-friendly substitute.

Cushing's Disease.

A super-rare condition called Cushings disease (only 10 to 15 people per million are affected, but 70 percent of those diagnosed are women) causes excess cortisol production and can trigger excessive weight gain just around the abdominal area (legs and arms usually stay lean) and the back of the neck, says Reshmi Srinath, M.D., assistant professor of diabetes, endocrinology, and bone disease at the Icahn School of Medicine at Mount Sinai.

Cushings typically presents with significantly low energy and complications like diabetes, high blood pressure, and high cholesterol. But the telltale sign is very large, red stretch marks on their belly, she says. If this sounds eerily familiar, talk to your doctor asap.

Dehydration

Theres a reason behind the bloat, and it may have just as much to do with the water you forgot to drink as the food that you ate.

Kristen Neilan , R.D., a dietician at University of Florida Health, says most of us arent drinking nearly enough water. Thats because many of us mistake the feeling of thirst for the feeling of hunger. Confusion, tiredness, and lightheadedness are all signs of even mild dehydration, she says. Sounds a lot like how we feel when were hankering for a snack.

Mixed signals arent the only only possible culprits behind your unexplained weight gain. Adequate hydration increases mitochondrial functionwhat that basically means is that it increases your metabolism, says Neilan. Without enough water, your cells cant do their thing (namely, convert your food into energy) quickly and efficiently.

Ovarian Cancer

In rare cases, an expanding belly is the result of an ovarian tumor and fluid buildup associated with it, says Dr. Sanaz Memarzadeh , M.D., Ph.D., a gynecologic cancer surgeon at UCLA Health.

Patients come in with abdominal bloating, and their usual pants are not fitting, she says. Sometimes the tumor is so large, it can cause dissention of the abdomen, says Memarzadeh.

Women are more likely to be diagnosed with ovarian cancer after menopause. But its important for women at every age to look out for this symptom, as well as feeling full too quickly, pain in the lower stomach area, and extra pressure on the bladder. See your doc if the bloating persists, especially if your family has a history of ovarian cancer.

You Quit Smoking

Smoking can often act as an appetite suppressant, so when you quit the cravings can hit strong. Pouya Shafipour, a weight loss specialist and doctor at Paloma Health , explains that smoking can lead to a rise in dopamine, the neurotransmitter responsible for instant pleasure. It's the same kind of pleasure you get when you eat a sweet snack, like ice cream.

Quitting smoking causes that dopamine level drop, but your cravings for it still remain, and this craving can sometimes lead to eating more than usual. "When one quits smoking, the body still has cravings for dopamine and often people get this craving from excess intake of refined sugar and starch (e.g. candy and other starchy snacks) and gain weight," says Shafipour.

To counteract the lower levels of dopamine once you quit smoking, it's important to engage in other behaviors, like exercise or meditation, that will cause a rise in the "feel-good hormone."

Diabetes

Type 1 and Type 2 diabetes both require insulin management in order to keep blood sugar levels regulated. In people with type 1, the pancreas essentially isn't producing enough insulin, so those that have it need to regularly insert themselves with the hormone. Insulin allows the body to absorb glucose (or sugar) and use it for energy.

Type 2 diabetes is associated with insulin resistance from a poor diet, a sedentary lifestyle, and unhealthy eating behaviors. That can usually contribute to weight gain in itself, explains Shafipour. Type 2 diabetics have a higher baseline insulin level which by itself causes more weight gain, typically around the belly (abdominal fat)," says Shafipour.

But an increase in insulin from external hormone treatments can also lead to weight gain. Insulin lets glucose into your blood cells so that it can be stored for energy, but if you're eating more calories than your body needs, your cells will take what they need leaving the remaining glucose to be stored as fat.

To counteract weight gain, it's important to closely monitor your diet and avoid eating too much fast food or foods high in refined sugar or diet, Shafipour says.

Cancer

Most cancers in their early stages will result in weight loss, instead of weight gain, unless it's a cancer that causes the release of cortisol, like a tumor in the adrenal gland.

However, as cancer progresses it can cause weight gain. "This weight gain can be due growth of the size of the tumor (e.g. ovarian cancer, stomach cancer), or metastasis to other organs like the liver which can cause fluid build-up in the stomach or the stomach cavity," says Shafipour.

But don't be too alarmed, as this is usually a worst-case scenario. Most cancers will cause other symptoms that may cause you to see a doctor while it's still in an early stage.

When Should I See A Doctor For Sudden, Unexplained Weight Gain?

First, you should take a look at what your lifestyle's like. If your diet is poor, it's normal to gain between a half a pound to a pound of weight a week. Your menstrual cycle can also caught your weight to fluctuate between four and five pounds depending on what stage of your cycle you are.

But when is weight gain a cause for concern? If you're gaining one to two pounds or more a week, and you don't see the numbers going down, then it might be time to see a doctor. "If one notices that they're gaining weight rapidly, one to two pounds a week, and it is not related to menstrual cycle, poor sleep, anxiety or depression, or snacking or over-eating, then they should probably see their primary care physician who will do a thorough history and physical as well as some appropriate laboratory work-up to find the causes of weight gain."

A doctor can work with you to determine whether an underlying condition is determining your weight gain, and find appropriate remedies to keep you at a healthy weight.